This invention relates in general to machine tools and relates more particularly to attachments for a milling machine.
In the figures, each element indicated by a reference numeral will be indicated by the same reference numeral in every figure in which that element appears. The first two digits of any 4 digit reference numerals and the first digit of any two or three digit reference numerals indicates the first figure in which its associated element is presented.
FIG. 1 illustrates a milling machine 11 that can be used to machine various workpieces. Such a machine can be utilized for many purposes including producing flat ends on workpieces, producing planar surfaces on workpieces, drilling holes, tapping holes and reaming holes. To perform such operations, this machine includes a chuck 12 into which can be inserted a variety of cutting tools 13 such as an endmill to produce flat ends, a flycutter to produce planar surfaces, a drill to drill holes, a tapping bit to thread holes and a reamer to size holes.
Milling machine 11 includes a milling table 14, having a top surface that is typically on the order of four feet long and fourteen inches wide, to which workpieces can be attached for application of various milling operations. Relative movement between the cutting tool and the workpiece is produced by rotating one or more of handles 15-17. Rotation of either of handles 15 produces movement of the table in the direction of the y-axis, rotation of handle 16 produces movement of the table in the direction of the x-axis and rotation of handle 17 produces movement of the cutting tool in the direction of the z-axis. A stop 18 can be positioned on a threaded shaft 19 to limit vertical (z-direction) movement of the chuck.
A top view of the milling table is shown in FIG. 2. The top of this table contains a groove 21 to enable various items, such as vice 31 of FIG. 3, to be clamped to the milling table. Vice 31 includes a base 32 in which are formed a set of notches 33 that enable the vice to be clamped to the milling table. The top edges of groove 21 overhang recessed portions of the groove. This enables devices such as vice 31 to be clamped to the table by the bolt assembly of FIG. 4. This bolt assembly consists of a bolt 41, a washer 42 and a nut 43 having projections 44 that fit into the recessed portions of the groove. Four of these bolt assemblies are used to clamp vice 31 to the milling table. Vice 31 also includes a pair of vertical blocks 34 and 35 attached to base 32. Threaded into a hole in block 34 is a crank 36 that can be screwed inward to clamp a workpiece between crank 36 and block 35. A workpiece can also be bolted into holes 37 in block 35.
This bolt assembly can also be utilized with a table clamp 51 of FIG. 5 to produce a clamp that is suitable for clamping a variety of workpieces directly to the milling table. Table clamp 51 includes an elongated hole 52 to enable an adjustable amount of overlap of table clamp 51 on top of a workpiece.
Unfortunately, for milling operations in directions other than parallel to the x-, y- or z-directions, the head 110 of the milling machine needs to be rotated to properly tilt the axis of the cutting tool to enable such a nonstandard milling operation. To rotate head 110 by an angle .theta. about the y-axis, a set of four locking bolts are loosened, a crank is inserted over the head of a bolt used to tilt the head, the crank is turned to bring the head to the approximate rotational orientation desired and then the accuracy of this direction is checked.
A scale 111 gives a rough indication of the angular rotation. The accuracy of this scale is insufficient for the precision operations typically required of a milling machine. The desired precision in the angular rotation .theta. is achieved by use of a sine bar 61, Job blocks 62 and indicator 71 illustrated in FIGS. 6 and 7. The sine of .theta. is determined from a trigonometry table and the required height H of Job blocks needed to produce this angle is calculated as L.multidot.sin .theta., where L is the length of the sine bar. A selection of Job blocks that totals H is placed under one end of the sine bar, thereby accurately rotating the sine bar by an angle .theta. away the horizontal.
To check whether the rotation axis of chuck 12 is perpendicular to the surface of the sine bar, shaft 72 of gauge 71 is inserted into the chuck, this gauge is bent at ball pivot 73 to form an angle .alpha., stop 18 is adjusted to allow tip 74 of the gauge to come into light contact with the sine bar and then the chuck is rotated to swing tip 74 in a circular arc about the rotation axis of the chuck. Indicator 75 will deflect by an amount indicative of the degree of deflection of tip 74 by contact with the sine bar. The amount of deflection at the points of minimum and maximum deflection indicate how far the rotation axis of the chuck is from being perpendicular to the top surface of the sine bar.
The four locking bolts are again loosened, the head is tilted closer to the desired angle, these locking bolts are again tightened and gauge 71 is again utilized to test for perpendicularity. It typically takes several iterations of this process to set the head rotation accurately at the desired angle .theta.. When the milling operations have been completed, this utilization of gauge 71 is repeated to orient the rotation axis of the chuck into a perpendicular relationship with the top surface of milling table 14.
The time involved in selecting the correct set of Job blocks can be avoided if the desired angle can be produced from some combination of "master angles". These master angles are wedges of metal that each has a pair of flat surfaces forming one of the master angles 0.25.degree., 3.degree., 4.degree., 5.degree., 6.degree., 10.degree., 15.degree., and 30.degree.. Because of the increasing frequency of requests by customers for nonstandard milling angles, it is becoming less common that the master angles can be used to set the orientation of the head.
Even when these master angles can be utilized, the entire process of setting the angle of the head is very time consuming. This process of precisely setting the angle of the head takes on the order of one-half hour. After completion of the milling operation, another half hour is required to orient the rotation axis of spindle 12 perpendicular to table 14. In addition to the monetary value of the time required for each rotation of the head, an additional monetary investment of about $1,200 is required for the sine bar and the set of Job block. Both costs are significant to a small machine shop. The cost of the Job blocks can be avoided if the only angles required are ones that can be produced by some combination of master angles. However, customers are requiring nonstandard angles more and more often so that even this expense cannot be avoided.
If the customer requires the production of several identical parts, then it can be cost effective to produce a jig that locates the workpiece at a particular position and that orients the workpiece at a particular angle. FIGS. 8 and 9 illustrate one such jig 81. This particular jig consists of a base plate 82 containing a set of holes 83 that enable it to be bolted to holes 37 in the vice of FIG. 3. Two sets of pins 84 and 85 are each positioned to position and orient an associated workpiece. Clamps 86 and 87 are utilized to hold the two workpieces 91 in place as illustrated in FIG. 9. The time and materials to produce such a jig can be justified only if the volume of parts to be machined using the jig is large enough that the cost savings in part production is more than the cost of producing the jig.
Circular parts also present a problem during milling operations. To prevent flattening the circular part and yet grab onto the part sufficiently firmly that the part will not turn during a milling operation, it is conventional to manufacture a set of "soft jaws". These jaw consist of a soft piece of metal into which have been formed a semicylindrical recess of diameter substantially equal to that of the round part that is to be milled. The cost of materials and time to manufacture such jaws can significantly increase the cost of milling operations on a single curved part or a small number of identical curved parts.